1. Field of the Invention
The present invention relates to a process for producing a polyorganosiloxane having structural units such as polysilsesquioxane and the like, suitably used as a polymer modifier.
2. Description of the Related Art
Polyorganosiloxanes having a polysilsesquioxane as main structural units have high mechanical properties, heat resistance and electrical insulation, and are therefore in wide use as a protective film in electronic parts and semiconductors, a material for interlayer insulation, a photosensitive material and a material for coating.
Polyorganosiloxanes are produced generally by a process which comprises subjecting at least one kind of organochlorosilane or organoalkoxysilane to a hydrolysis and condensation reaction. Since organoalkoxysilanes are produced from organochlorosilanes, it is obvious that use of an organochlorosilane(s) as a material(s) for production of polyorganosiloxane can produce a polyorganosiloxane at a lower cost.
Many techniques have been reported for production of a polyorganosiloxane from an organochlorosilane(s), and an introductory article on such techniques is given in Chem. Rev. 95, pp. 1409-1430 (1995) by R. H. Baney et al. In this introductory article, it is described that polyphenylsiloxanes having an average molecular weight of 10,000 to several tens of thousands were synthesized from phenyltrichlorosilane by, for example, Brown et al. or Adachi et al. Techniques for synthesizing a polymethylsiloxane from methyltrichlorosilane are disclosed in Japanese Patent Publication No. 17214/1985, U.S. Pat. No. 4,399,266, EPO No. 0406811A1, etc., and it is described in these literatures that polymethylsiloxanes having an average molecular weight of 10,000 to several tens of thousands were produced.
Meanwhile, in Japanese Patent Application Laid-Open No. 157605/1996, etc., it is described that in synthesizing a polyorganosiloxane from methyltrichlorosilane or vinyltrichlorosilane and also in synthesizing a polyorganosiloxane by copolymerizing methyltrichlorosilane or vinyltrichlorosilane with other trichlorosilane, gelation takes place easily during the synthesis and, even if the gelation can be avoided, the resulting polyorganosiloxane is very unstable.
Preferably, polyorganosiloxanes having a polysilsesquioxane as main structural units, when used as a resin modifier or as a material for coating, have a low viscosity for easy handling, has a high content of a reactive group (e.g. a silanol or a functional group), and has a low molecular weight for easy dissolution in solvent or for other reasons. Polyorganosiloxanes having a low molecular weight of several thousands are in production in some cases, as described in Japanese Patent Application Laid-Open No. 227321/1991 or Japanese Patent Application Laid-Open No. 157605/1996. In production of such a low-molecular polyorganosiloxane, a two-phase (aqueous phase and organic phase) interface reaction is used. In this reaction, stirring must be made so that the aqueous phase and the organic phase are not disturbed, which imposes an operational restriction. Further, in the reaction, a large amount of a neutralizing agent (an alkali metal carboxylate) is required, resulting in a higher production cost. The reaction has a further problem in that there is a limitation in the mixing ratio of an alkyl group-containing silane compound and an aromatic group-containing silane compound. Therefore, technical improvements are desired.